A roller mill of the aforementioned kind is known for example from U.S. Pat. No. 4,828,189. This known mill is a so-called vertical mill and comprises a casing or mill body with a horizontal grinding table positioned within the mill body mounted for rotation about a vertical axis. Drive means such as a motor and a gear reducer, situated beneath the grinding table, are provided for rotating the grinding table. Rocker arms are mounted in the roller mill structure and in the end of each rocker arm a grinding roller is mounted for rotation about an axis, which is situated at a predetermined angle to the table. The load-carrying mill structure is assembled from a plurality of mill stands, one for each grinding roll. Each grinding roll assembly, consisting of a grinding roller, axle, hub and bearing, requires a mill stand to support the force mechanism, such as a hydraulic cylinder, which generates the grinding pressure and which is mounted in the mill stand.
It is essential to have the ability to remove a mill's gear reducer, as its components are subject to heavy stress loading and therefore may need to be occasionally replaced. As the mill stands are main parts of the structure and heavily stressed, they are usually welded together and, with the mill body, permanently fixed into the foundation, for example by epoxy grout and foundation anchor bolts. Because of this, vertical mills are generally limited to a maximum of four permanent mill stands, one for each grinding roll assembly, as the space between the mill stands otherwise will be too narrow for replacement of the gear reducer. While possible, it is not ideal to remove one of the mill stands in order to replace or repair the gear reducer.
Alternately it is possible to increase the number of mill stands, and thereby the number of grinding rollers, by moving the mill stands significantly outwards. This typically requires that the other mill components such as roller axles, grinding table and rocker arms become much larger. The higher costs due to such an increase in component size counteract any profit gained due to the mill capacity increase realized by increasing the number of grinding rollers. A different means of providing more grinding rollers is therefore desirable.